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Publication Abstract from PubMed

The genomes of some purple photosynthetic bacteria contain a multigene puc family encoding a series of alpha- and beta-polypeptides that together form a heterogeneous antenna of light-harvesting 2 (LH2) complexes. To unravel this complexity, we generated four sets of puc deletion mutants in Rhodopseudomonas palustris, each encoding a single type of pucBA gene pair and enabling the purification of complexes designated as PucA-LH2, PucB-LH2, PucD-LH2, and PucE-LH2. The structures of all four purified LH2 complexes were determined by cryogenic electron microscopy (cryo-EM) at resolutions ranging from 2.7 to 3.6 A. Uniquely, each of these complexes contains a hitherto unknown polypeptide, gamma, that forms an extended undulating ribbon that lies in the plane of the membrane and that encloses six of the nine LH2 alphabeta-subunits. The gamma-subunit, which is located near to the cytoplasmic side of the complex, breaks the C9 symmetry of the LH2 complex and binds six extra bacteriochlorophylls (BChls) that enhance the 800-nm absorption of each complex. The structures show that all four complexes have two complete rings of BChls, conferring absorption bands centered at 800 and 850 nm on the PucA-LH2, PucB-LH2, and PucE-LH2 complexes, but, unusually, the PucD-LH2 antenna has only a single strong near-infared (NIR) absorption peak at 803 nm. Comparison of the cryo-EM structures of these LH2 complexes reveals altered patterns of hydrogen bonds between LH2 alphabeta-side chains and the bacteriochlorin rings, further emphasizing the major role that H bonds play in spectral tuning of bacterial antenna complexes.

Cryo-EM structures of light-harvesting 2 complexes from Rhodopseudomonas palustris reveal the molecular origin of absorption tuning.,Qian P, Nguyen-Phan CT, Gardiner AT, Croll TI, Roszak AW, Southall J, Jackson PJ, Vasilev C, Castro-Hartmann P, Sader K, Hunter CN, Cogdell RJ Proc Natl Acad Sci U S A. 2022 Oct 25;119(43):e2210109119. doi: , 10.1073/pnas.2210109119. Epub 2022 Oct 17. PMID:36251992^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.